1. Field of the invention:
This invention relates to colloid mills having an enclosure in which a rotor turns relative to a stator and wherein a slurry passes between the elements to produce a fine colloid. A cooling fluid is provided to both the stator and rotor through annular passages therein to avoid problems with excessive heating of the mechanical elements as well as the slurry itself.
2. Description of the Prior Art:
A number of industries require milling to refine a product to increase its utility. Typical products are foodstuffs, paints, toiletries and pharmaceuticals. Early mills mixed the product to be refined with pebbles or balls, and rotated the mixture such that the pebbles or balls crush and mix the solid particles. Other mills use rollers, generally in pairs, through which the slurry is passed and crushed or ground. More recently colloid mills have been developed which use a rotor turning relative to a stator with the slurry to be milled continuously passing through the narrow space between the rotor and stator. The rotor smears a thin film of the slurry on the cooperating stator face and the hydraulic shear effect produced by the interaction of the two elements produces emulsions characterized by particle sizes ranging down to submicron.
To produce small particle sizes it is necessary to make the space between the rotor and stator quite narrow, and/or to drive the rotor at relatively high speeds. With increased speed and shearing force, slippage of the slurry occurs and undesired heat builds up. For some products, particularly chemical and biological products, heat is destructive, and heat is always detrimental to seals and precision mechanical elements.
It has been suggested in the prior art to prevent heating problems by cooling the colloid mill. For example, in U.S. Pat. No. 3,814,334 to Funk, a colloid mill of the type that uses pebbles or balls is supplied with a cooling jacket around the rotating elements. U.S. Pat. No. 3,788,565 to Adams injects a flush fluid to protect and cool a mechanical seal for the rotor shaft of a colloid mill. And U.S. Pat. No. 4,113,189 to Sullivan states that heat problems in conventional colloid mills are often avoided by increasing the gap between the rotor and stator, which has the undesirable result of reducing the efficiency of the mill and the amount of refining that occurs, or by cooling the rotor, the stator, or both, although no means is shown to accomplish the cooling.
It is also known to be common practice to provide a cooling fluid to cool the stator of rotating devices such as colloid mills.
It is an object of the present invention to provide improved cooling to conventional colloid mills to prevent unnecessary and detrimental heating of the colloid mill elements as well as the slurry passed therethrough.
A further object of the present invention is a novel system and apparatus for cooling the rotor of a colloid mill.
A still further object of the present invention is an improved cooling system for colloid mills in which a cooling fluid is supplied continuously to both the rotor and stator during operation thereof.